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y 1940. s. L. CLOTHIER :1- AL 2,201,811

acumen Filed June'l, 193a 2 Sheets-Sheet 1' INVENTORS ATTORNEY May-21,1940.

' s. 1.. CLOTHIER El AL 2,201,811

SCANNER Filed June 1, 1938 2 Sheets-Sheet 2 I INVENTORS 5 TzM/A/a 7 z.(jam/2'2 ATTORNEY Patented May 21, 1940 UNITED STATES PATENT OFFICEHogencamp,

Irvington,

N. J., assignors to Kolorama Laboratories, Inc., Newark, N. J., acorporation of New Jersey Application June 1, 1938, Serial No. 211,142

5 Claims. (01. 178-16) This invention relates to scanning mechanism andmore particularly to electromagnetic means for oscillating a pivotallymounted mirror.

In television scanning systems, oscillographs, and the like, it is oftennecessary to periodically produce an angular deviation of a mirror inresponse to electrical impulses. The results are often times obtainedthrough the use of a magnetically permeable armature connected to anoscillatable mirror, or through the use of a properly designed rotatingcam and follower mechanism suitably connected to the mirror.

Moving armatures oscillated by the intermittent electrical impulses havethe disadvantage of having relatively great weight and the attendantdisadvantage of being unable to respond to high frequency electricalimpulses because of the inertia of the moving parts. Cams have provensatisfactory as a driving medium but they are subject to thedisadvantage that they are relatively expensive to fabricate and themotion produced is limited strictly by the design of the cam.Furthermore, such cams are exposed to. wear, they must be rotated atconstant speed, and they operate with relatively high inertia.

In the present invention it is proposed to utilizethe flexibility of theelectrical wave-form to obtain any desired mechanical wave form.

The objects, therefore, of the present invention are: to provide animproved scanning mechanism operable by electrical impulses; to providein such a mechanism mirror-oscillating means having a minimum inertia tomotion; to provide in such mechanism means comprising a moving coil forreaction with the electrical impulses; to provide improved means forflexibly connecting the moving coil with the mirror; and to providemeans for minimizing chattering of the device at operating frequencies.These and'other objects will become more readily apparent from thefollowing description in conjunction with the appended drawings showingone form of scanning mechanism incorporating the present invention.

In the drawings:

Fig. 1 is a vertical sectional view taken through the improved scanningmechanism;

Fig. 2'is a sectional view taken on the line 2-2 of Fig. 1;.

Fig. 3 is a detail sectional view taken on the line 33 of Fig. 2; and

Fig. 4 is a view of a modified form of mirror connecting means.

Briefly, the invention comprises a magnet and coil construction of atypesimilar to that employed with dynamic loudspeakers. .A. magnet Mgenerates magnetic lines of force across an air gap, preferably ofannular shape, and a moving coil C assembly corresponding in design withthe voice coil of a dynamic loudspeaker is located within the annulargap so as to intercept the magnetic lines of force. A connecting link Lextends from the moving coil assembly to a pivotally mounted mirrorassembly P in such a way that movement of the coil imparts an angularmotion to the mirror about the axis of the pivotal mounting.

Referring now in greater detail to the drawings, the magnet M comprisesa permanently magnetized core structure II of steel, nickel-iron alloyor other suitable material having high permeability and rententivity.The core structure I I, as shown in the drawing, comprises an annularshell I2 having a centrally located pole-piece I3 mounted to a bridgingtop plate I4. An annular base plate I5 is secured to the shell I2 so asto complete the magnetic path with the bottom of the pole-piece I3through an intermediate air-gap I6 preferably of annular shape. The baseplate I5 is relatively thick and its central aperture is dimensionedsoas to be but slightly larger than the diameter of the pole-piece I3 sothat the annular magnetic path formed comprises a deep space with but anarrow gap between the adjoining parts so as to provide an intenseradial magnetic field in the air gap. A tubular dome ll of non-magneticmaterial such as cardboard, fiber, or the like extends within the airgapclosely about the pole-piece I3 and is provided with a winding of smallinsulated wire about its outer periphery, the terminals I9 of whichextend downwardly from the dome I! for connection with a source ofelectrical impulses. The dome I! is supported by a diaphragm 2| of paperor the like preferably provided with a series of annular corrugations,which diaphragm permits the coil to move in an axial direction butinhibits its motion transversely. The diaphragm 2I is secured directlyagainst the base plate I5 by means of a clamping ring 22. The movablecoil C comprising the dome I1 and the winding I8 is joined with thepivotally mounted mirror P by means of the connecting link L comprisinga stem 23 secured at the base of the dome I 1 by means of a machinescrew 24 and reinforcing Washers 25. The stem is slidably mounted withina bushing 26 disposed axially about the stem in spaced relation to thedome II. The bushing is firmly secured within a support 21 extendingfrom the base plate I5.

The pivotally mounted mirrorP comprises a a sheet of reflecting materialsuch as polished metal, silvered glass, or the like firmly secured to aspindle 30, having axially located sockets 31 at the respectiveextremities thereof. A pair of pivot mounting blocks 32 are secured to abase member 33 as by screws 34. Pivots 35 preferably comprising threadedrods having hardened conical points 36 extend through the blocks 32 intothe respective sockets 3| at each end of the spindle 30. The pivots 35are adjusted until the spindle pivots freely without lost motion, atwhich time locknuts 31 are tightened to hold the pivots in the adjustedposition. A radius arm or pivoting link 38 is tightly secured to thespindle 30 as by means of a locking screw 33. The radius arm 38 connectswith the stem 23 through a resilient link 4| preferably comprising athin strip of tempered spring steel secured in any convenient manner atits opposite ends to the stem 23 and the arm 38. The magnet M issupported in fixed relation to the base member 33 by a plurality of legs42.

The device operates as a scanning mechanism by projecting a beam oflight upon the pivotally mounted mirror P and attaching the terminals l9to the source of electrical impulses. Presuming for example that theelectrical impulses comprise intermittent surges of electric current asan alternating current sine-wave, the current passing through thewinding l8 exerts alternating impulses in the highly concentratedmagnetic field in the air-gap l6 with the effect that the movable coil Cis subjected to an oscillating motion along the axis of the stem 23.This motion is imparted through a resilient link 6| to the radius arm 38causing the pivotally mounted mirror P to oscillate angular-1y, thusimparting the desired scanning motion to the reflected light beam. Withan exciting impulse of sine-wave shape, the miror is oscillatedsubstantially according to simple harmonic motion. As the arm 38 pivotsfrom the horizontal position shown in Fig. 1 its lateral distance fromthe stem 23 decreases. This motion is of such small magnitude, however,that it is compensated for by fiexing of the link 4|. At the same timethe tendency for the flexible link to return to a straight positionmaintains the parts under a slight tension and operates to minimizechattering when the device is in operation.

In Fig. 4 a slight modification of the connecting link L is shown.Instead of the resilient link 4| use is made of a flexible cable, cord,or chain 43 which is operative to lift the radius arm 38 whenever thestem 23 is raised, and a helical tension spring 44 is secured to the arm38 so as to return the arm to the lower position whenever such motion ispermitted by a corresponding lowering of the stem 23. With the modifiedarrangement there is less tendency for a sideways force to be exertedagainst the stem 23 as might be exercised by a resilient link 4|, whichpressure may increase the friction between the stem 23 and the bushing26 if the angular motion is excessive.

It will be noted that the, magnetic forces of the moving parts areobtained without the use of an iron armature or its equivalent, and theweight of the moving parts has been maintained at a minimum. Therepulsion and attraction is obtained through the use of a light-weightmoving coil which provides for accurate response even at comparativelyhigh frequencies of the electrical impulses, as the moving parts do notpossess the high inertia of an iron armature. Furthermore, theelimination of iron from the moving parts eliminates hysteresis as afactor limiting the frequency of operation. Since the designincorporates features of the dynamic loudspeaker the limiting operatingfrequency may be estimated roughly as the highest pitch note to whichsuch type of speaker responds, as the inertia of the oscillating mirrorand the connecting link does not differ materially from the mechanicalinertia of the usual paper cone. A dynamic speaker may be converted touse in the improved scanner by removing the cone from the unit, and bysuitably connecting the mirror to the moving coil assembly,

In practice we have found that at all ordinary television frame-scanningfrequencies, this device readily reproduces mechanically the wave-formof the exciting current, irrespective of its shape. For example double,and even single sawtooth wave-forms are faithfully reproduced.

It will be appreciated, of course, that while a T magnet of thepermanently magnetized type has been shown, electromagnetic units forgenerating the annular fiux field may be employed equally well.

The corrugated diaphragm 2| herein described exerts a steadyinginfluence on the motion of the coil assembly. The inertia of thisdiaphragm may be lessened by forming lightening holes therein, or thediaphragm may be formed as a spider having radial supporting armssimilar to the support 21. In some cases the diaphragm may be eliminatedentirely, rendering the device more sensitive at high frequencies.

Obviously, the connection between the mirror and the moving coil may beof any suitable de sign. The dome disclosed is desirable in that itprovides a rigid connection having light weight.

Various other changes will suggest themselves to one skilled in the artwithout departing from the scope of the invention or sacrificing any ofits advantages.

We claim:

1. In combination a dynamic unit having a coil movable in an annularmagnetic field and responsive to electrical impulses, a member connectedfor movement axially with said coil, a pivotally movable scanningmirror, and means connecting the said member and mirror to oscillate thelatter and compensating for the arcuate movement of the mirror intranslating the linear movement to oscillating motion.

2. In combination a dynamic unit having a coil movable in an annularmagnetic field and responsive to electrical impulses, a member connectedfor movement axially with said coil, a

pivotally movable scanning mirror, and flexible means connecting thesaid member and mirror to oscillate the latter and compensating for thearcuate movement of the mirror in translating the linear movement tooscillating motion.

3. In combination a dynamic unit having a coil movable in an annularmagnetic field and responsive to electrical impulses, a member connectedfor movement axially with said coil, a

pivotally movable scanning mirror, and resilient .1.

means connecting the said member and mirror to oscillate the latter andcompensating for the arcuate movement of the mirror in translating thelinear movement to oscillating motion.

4. In combination a dynamic unit having a coil movable in an annularmagnetic field and responsive to electrical impulses, a member connectedfor movement axially with said coil, a pivotally movable scanningmirror, and leaf spring means connecting the said member and pivotallymovable scanning mirror, and means connecting the said member and mirrorto oscillate the latter and compensating for the armate movement of themirror in translating the linear movement to oscillating motion andtension means assisting the oscillatory movement.

STEWART L. CLOTHIER. HAROLD C. HOGENCAMP.

